The functions of a purified Ca2 ion-binding protein of brain will be evaluated in the proposed research. This Ca2 ion-binding protein has been identified as a multifunctional Ca2 ion dependent regulator (CDR) believed to couple intracellular Ca2 ion transients to diverse functional changes in various cells. CDR has been shown to modulate in vitro adenylate cyclase, cyclic nucleotide phosphodiesterase, protein kinase and histone phosphatase activities as well as to stimulate the active transport of Ca2 ion by erythrocyte plasmalemma and cardiac sarcoplasmic reticulum. The proposed investigations focus on its modulation of histone phosphatase activity and examine the possibility that CDR regulates active transport of Ca2 ion in brain synaptic vesicles by a phosphorylation mechanism. The approach to be pursued includes the following areas of investigation: (1) the purification to homogeneity, physical and kinetic characterization of a brain CDR-modulated histone phosphatase activity; (2) the examination of selectively phosphorylated histone components of intact Chinese hamster ovary cell chromatin as substrates for a brain CDR-modulated histone phosphatase; (3) the comparison of CDR-modulated histone phosphatase activities from CHO cells and brain; and (4) the correlation of the phosphorylation of brain "coated" vesicle membrane components with the Ca2 ion transport activity of the vesicles.